The proposed research is an extension of ongoing investigations of the role of intercellular communication in the regulation of neuronal growth and development. These studies will examine the biochemical consequences of neurotransmitter interactions, and the role of such interactions in neuronal phenotypic expression. The rat sympathetic superior cervival ganglion (SCG) in vitro will be used to study the influences of peptide transmitters on sympathetic phenotypic expression, and conversely to examine mechanisms regulating expressions of peptidergic triats by autonomic neurons. More specifically, we plan to: a) Characterize the effects of the peptide neurotransmitters, substance P (SP), somatostatin (SS), and vasoactive intestinal polypeptide (VIP) on the development of noradrenergic traits in sympathetic neurons; b) Define factors regulating the expression of the SP, SS, and VIP phenotypes by sympathetic neurons; c) Examine the role of intercellular interactions in peptidergic expression by sympathetic neurons. In a broader sense, these studies seek to define the molecular basis of neurotransmitter mutability and synaptic plasticity. It is hoped that such studies may indicate biochemical loci where therapeutic intervention in disease processes may lead to a return to normal neuronal function.